Electronic bit tester



June 16, 1953 R. s. SEGSWORTH ELECTRONIC BIT TESTER Filed Jan. 31, 1950 M) lllll mimn'ron Foam; 5. siaswaem Patented June 1 6, 1953 UNITED STATES-- PATENT OFFICE? ELECTRONIC BIT TESTEBn Robert Sidney Segswortlifliironto; Ontario, Canada Application January 31, 1950, sesame-141,454 i Figure" 1 'isia'schematicof the basic circuit,

diagram of the instrument of the irivention'illustratingprinciples embodiedin'the testing method.

Figure 2 is. aschemati'c ofapracti'cal' form of instrument according it'oith'e' invention? Ifi'Fi'gure 1 anoscillator circuit is shown wherein the triode H1 or other suitable electronic amplifier has a resonant circuit "comprising the coil H and condenser l2 'connecti'ngto the anode l3 being in" the plate circuit of thesaidf tube and connected to a source. of voltage M in the conventional manner." The-cathode [5 has a resistor and condenser combination IS in series withlthe same toi'the negative side of the voltagesupply [4 to provide suitablebiaslfor the gridfll; The feedback coil [8 to "grid IT "a variable in itscoupling to the primary coil .II by the test sample l9 which is of a-magnetically'permeable material.

According to the invention the outputfof the oscillator "is measured from' th'e -grid. side: such" as 5 Olain'1's; (015175 483) by a suitablevoltmeter-'20 whicn ior'therequired sensitivity sh'ouldbeof'th'e electronic type;-

The principle'involve'd in the present-invention is the control 0f -fe'ed--back*in "the oscillation'cirs cuit from'th'e primarycoilfll to these'condary coil! 8 in combination with the measuring Offth voltage across" the grid-side 'of the "circuit where-- by 'the output "measured is highly sensitive to the magnetic properties of the-'testpiece I9.

In providing-an instrument' of practi'cal form With' 'resistor 26 isemplo'yed inparallelitherewith to showwhentheoscillatorsisoperatihgl Positive voltageissuppliedthroughthe liiie zfir'om a suitable power supply 28"having, a..l nown rectifier tube arrangement. 29-and-Y;filter device .30. The secondarycoil'f3 'f has a large :number oflturns as .compared with'. the primarygbutincludes atap 32 "connecting by ,a line' 33lto thecontrolg-rid, the tapIb'eirig ,ld'catd toiprovide vsufficient voltage to operate thegridg The .cathodenresistors '34; ,3-5 and '36and'bypass condenser 3l-"a're usedtto provide' appropriatebiasie. Resistor i36,;however,' in cludes a switch device 38 'Which'is manuallytoperable for providihgga sudden change inbiasinthe tube 2 I in order to-initiate..osci11ation in-a man-- ner hereinafter describedinmore detail."v

A test sample ,such'. as the bit' 39 illustrated,

makes magneticconta'ct with the polepieces '40 and 41 by manual. placement, the pole piecesbeing in magnetic circuit relation with the coils 22 and 3|. Itiwill be appreciatedithatthe potential generated in the coil '3 I will be greatly reduced whenthe magnetic circuit is opened -by removing a'bit fr'om'the test positions and,'accordingly', sublstanti'al changes must be made in the circuit to sustain oscillation. Thesechanges are accomplished by'm'eans 10f airelayo-fl such; that when the -test piece is' removed the polepiece 4 I is removed'from'ele'ctri'cal 'contactwith' the. polelcontact"43" therebyshbrtingythe resistor 44 Whichi is of hig'l if'va'lueias nomparedmithi the resistorp45. Theterminal encl'46 of resistor 45 electrically connects to the 'fiiam'ent supply coil'll of the low voltage "transformer 48Tas at 46a; Filament sup: ply voltage or 'othersuitable supply vvoltage" may, therefore, be .applied across the relay, to ground but therelay fl isprdinarilyjin serieswitha re-- sistorM-Ot high value across this supply voltage, and therefore; does not'rec'eive sufiicient current to beenergizediwhenth'e magnetic circuitiisaopen. However; whenithe testsampleis in place thepole piece 41 makes contact withthe contact 43 shorting-out the resistor andfth'ereby ,prov'idingtenergizationor theme-lay; coil 4 9 1 As, the v latter is energized therelay contacts Eliand 5] which are grounded as at 52"a're"opene'd; and the full "value of -resistor""3'5 comes: "into "effect in"determining thebias on" the "grid'23diofthe tube "2 l When the "bit- 'or'test' piece 39"is removed the: relaytcon tacts close, the'contact 50"th'erebyJ reducing the bias-and*the-valuerofthe resistor '35 "on'the tube 2i) If oscillation'shouldcease the closing of the momentary "switclit my manual operation results ina substantialfi'eduction in'the cathode resist anceoftheosci'llator tube 21 causing asurge. of current which? starts the oscillator,

In respect tothe measuringiof the outputot the'oscillatdr a suitable amplifier 53 has a suitable filter arrangement 54 of known type in its plate circuit and embodying a resistor '55 across which the voltage is measured by a suitable voltmeter 56. The anode 57 obtains operating voltage through the filter and resistor 55 by the line 58 connecting by suitable voltage dropping resistor 59 to the line 27. The voltage dropping resistor 60 extending from line 58 determines the screen voltages of the screen grids 6| and 62 of. the tubes 21 and'53 respectively; The sensitivity of the instrument to fluctuations in line voltage may be reduced by providing the voltage regulator tube 63 and condenser 64 in parallel therewith from the scren grids to ground in the manner shown. A suppressor grid 65 of the amplifier .53 i connected directly to the cathode 66 thereof and the cathode is adjustable in its bias through the potentiometer 61 placed in a voltage divider cir-- cuit from the screen by being connected in series with the resistor 68 extending from the screen grid 62. A suitable condenser 69 for the desired by-pass is included.

The control grid 10 of the amplifier tube 53 is coupled to the high end ll of coil 3| through the coupling condenser 12 and a pair of grid resistors 13 and M are connected in series to the ground point 15. However, when the bit is removed as previously discussed the signal reaching the grid will rise appreciably and in order to compensate for this condition and avoid damaging the meter the contact 51 is closed and the resistor 14 is shorted leaving only the resistor 13 to determine the voltage on the grid 70. It will be noted that not only do the resistors 44 and 45 serve as a voltage divider but also prevent the inductance of the relay coil 3| from building up a high potential across the pole pieces 40 and 4| whenever the relay circuit 42 is opened.

The adjustment of the resistor 34 in the oathode circuit of the oscillator tube 2! is all that is required to compensate for variations in line voltage, wear on the pole pieces, and to provide an appropriate setting for any particular size of 'bit. The potentiometer. 61 controls the bias on the voltage amplifier tube 53 and thus may be employed to change the meter reading independently of the field as controlled by the variable resistor 34. The variable resistor 35 in the cathode circuit of the oscillator 2| is employed to adjust the field strength during the period when a'test sample is not placed in contact with the pole pieces 40 and ll. This control is adjusted in the following manner.

The'oscillator is started by shocking the circuit through the closure of the manual switch 38 and a bit sample is placed in contact with the pole pieces 40 and'4l. The variable resi tor 34 is adjusteduntil the meter 56 gives the desired reading for that bit.

The bit is then removed and in order to ensure that the oscillator will continue operating even though a defective contact is made the bit is again placed in contact with the pole pieces but through a sheet of paper or other suitable nonmagnetic material of consistent thickness providing a predetermined gap between surfaces of the pole pieces and the test sample. The variable resistor 35 is thenadjusted until the meter reads approximately zero. Thi method of adjustment will provide sufficient field to sustain the oscillator without damaging the meter and at the same time ensure that the test piece will give a defective reading if it is not makingproper contact with the pole pieces 40 and 4|.

For the sake of simplicity the meter may have 'area will indicate an acceptable contact of the bit with the pole pieces 40 and ti. In general, however, it will be found that satisfactory bits having the desired hardness will read in the green area and the softer bits will read in the red area.

The device of this invention is of the comparator class and-referenceinustalways be made to standard samples wit l f known characteristics. Operation depends upon magnetic properties and is, therefore, effected by mass, condition of contact,length of magnetic path involved and other factors;

The pole pieces 49 and 4! are of particular importance in respect to the contact surfaces thereof and it is necessary to provide substantially similar contact with samples of various dition of the samples. However, in regard to any one series of samples of the same dimensional characteristics spherical contact surfaces on the pole pieces have been found very desirable and these may be in the form of nodules or fingers with spherical tips lying into the recesses about the cutting edges of the bit.

Although the device herein disclosed is operable over a relatively high range of frequencies, the skin effect" experienced in the test sample is a factor which must be taken into account and limits the best response to relatively low frequencies. Thus, in testing rock drilling bits for hardness, a frequency 'of about eighteen cycles per second has been found to give the best results.

It is intended that this disclosure should not be construed in any limiting sense aside from that indicated by the scope of the following claims. r

What I claim as my invention is:

1. In a device for comparatively testing the hardness of magnetically permeable test samples of similar dimensional characteristics and employing an electronic circuit including an oscillator tube having at least a plate, a grid, and a cathode, and magnetic coupling means between the circuit of the plate and the circuit of the grid, the combination therewith of, a primary coil in the plate circuit 'and a secondary coil in the grid circuit including pole pieces associated with each of said coils and forming said magnetic coupling means, said pole pieces being shaped to contact surfaces -of a test sample of magnetically permeable material, means associated with said primary coil providing a predetermined frequency of resonance of less than 60 cycles per second in the plate circuit, means for biasing said grid to, provide oscillation in said oscillator when thetest sample is in physical contact with said pole pieces, and a voltage measuring device including anamplifier tube coupled to the grid circuit of said oscillator tube, said voltage amplifier having an electronic tube including at least a grid, a plate, and a cathode, and adjustable grid biasing means for said amplifier grid whereby the current flowing through said amplifier tube may be-adjusted to zero when a test sample is disposed outside the efiective magnetic field of said pole pieces, and

means for controlling the biasingmf the grid-1.01 saidoscillator tube whenzthe test :sample-ds so disposedto sustain oscillations-inxsai'd oscillator whereby said voltage measuring-device :is responsive to the increase in: :voltage :developed; the grid circuit. of said; oscillator whenathei test sample is -placed..in physical contactrwithlsaid pole pieces to: close .thexmagnetic:circuit f said coils..

2. In a device for comparatively testingi zthe hardness of magneticallypermeable test samples of similar dimensional I characteristics Lt-andt'employing an electronic circuitfincluding- -zani oscillator tube having at least a plate, a grid, an'dla cathode, and magnetic:coupli'ngmeans between the circuit of the plate and the circuit of the grid, the combination therewith of z' a prim'ary coil in the plate-circuitiand a' secondary coil in thegrid circuit, pole pieces in each of said coils defining a magnetic core, an opening in said core adapted to be closed 'by a test sample of magnetically permeable'material to physically close the magnetic circuit'tofsaid coils,v means associated with said primarygcoilproviding a predetermined frequency of resonance of a value less than 60 cycles per secondlin the .platecircuit, means for biasing said grid to provide-oscillation in said oscillator when the test sample-sis in physical contact with said pole pieces, and a voltage measuring device for measuring at least a part of the voltage between said grid and said cathode.

3. In a device for comparatively testing the hardness of magnetically permeable test samples of similar dimensional characteristics and employing an electronic circuit including an oscillator tube having at least a plate, a grid, and a cathode, and magnetic coupling means between the circuit of the plate and the circuit of the grid, the combination therewith of a primary coil in the plate circuit and a secondary coil in the grid circuit, pole pieces in each of said coils defining a magnetic core, an opening in said core adapted to be closed by a test sample of magnetically permeable material to physically close the magnetic circuit of said coils, means associated with said primary coil providing a predetermined frequency of resonance of a value less than 60 cycles per second in the plate circuit, means for biasing said grid to provide oscillation in said oscillator when the test sample is in physical contact with said pole pieces, a voltage measuring device for measuring at least a part of the voltage between said grid and said cathode, the biasing means for said grid comprising a resistor in the cathode circuit of said tube electrically in series with the cathode and plate thereof across a source of supply voltage wherein positive voltage is supplied to the plate and the negative terminal of said source is connected to one end of said resistor, the other end being connected to said cathode, and means for reducing said resistance to a value to sustain oscillations in said oscillator when the test piece is removed from said pole pieces comprising a relay having a normally closed contact through which a point between the ends of said resistor may be connected to the negative terminal, a relay coil for actuating said contact and causing opening thereof, a separate source of energy for energizing said relay coil, a voltage divider across said source of energy, and means for connecting said coil to a small voltage portion of said voltage divider, and an electrical switch actuable when a test sample is in physical contact with said pole pieces; andcconnected:;electricallyyacrossiiaelarge voltage-portion iof zsaid :voltagei-dividerwvhereby 4 said contact;istopenionly-rwhenzsaid;relayaisxen ergized by engagementota test sample; withisaid pole-pieces I ,t 1 4:: In ,a device sforrcomparatively testing:the

hardness?ofmnagneticallyapermeable:testisamples of similar; dimensional,rcharacteristicsiandiiemploying :an' electronic acircuit including; an:oscilvlatomtubeahavingaat leastia plate; a1grid;;.and :a cathode; andtmagneticctcouplingsmeans 'between the iClIfCllitFlOf the platerandiltheicircuitlofsjthe gridLthe combinationztherewithinf:. a" primary 'coil in the. -:p1ate-;:circuit:andcaisecorrdary'vcoilfiiir'the gridlcircuit;,pole xpieces:in.:eaclittofa said coilsisdefininggvatmag-netidicore,s .ani opening 'inzlsaid core .adaptedztcr.bezclosedl byuza-ztestersampler-ofs1 magnetically ,permeableezmaterialetw physically close theanagrretid: circuitottzsaidtcoils; means "associ- .atedawith said :primarymoil. promding'a spredeter- 'meansrsfor said-giiidwcomprising a resistor in-th'e cathode circuit of said tube electrically in series.

with the cathode and plate thereof across a source of supply voltage wherein positive voltage is supplied to the plate and the negative terminal of said source is connected to one end of said resistor, the other end being connected to said cathode, and means for reducing said resistance to a value to sustain oscillations in said oscillator when the test piece is removed from said pole pieces comprising a relay having a normally closed contact through which a point between the ends of said resistor may be connected to the negative terminal, a relay coil for actuating said contact and causing opening thereof, a separate source. of

' energy for energizing said relay coil, a voltage divider across said source of energy, and means for connecting said coil to a small voltage portion of said voltage divider, and an electrical switch actuable when a test sample is in physical contact with said pole pieces and connected electrically across a large voltage portion of said voltage divider whereby said contact is open only when said relay is energized by engagement of a test sample with said pole pieces, said voltage measuring device comprising an electronic amplifier tube having at least a plate, a cathode, and a grid, means for biasing said amplifier grid including a variable resistor in the cathode circuit of said tube, means coupling the primary coil of said oscillator to the grid of said amplifier tube including a grid resistor of predetermined value extending between the grid and said negative terminal and a second normally closed contact openable by energization of said relay connected between the ends of said grid resistor and said negative terminal to reduce the voltage applied to the grid of said amplifier tube when the test sample is removed from engagement with said pole pieces.

5. In a device for comparatively testing the hardness of magnetically permeable test samples of similar dimensional characteristics and em--v ploying an electronic circuit including an oscillator tube having at least a plate, a grid, and a cathode, and magnetic coupling means between the circuit of the plate and the circuit of the grid, the combination therewith of: a primary coil in the plate circuit and a secondary coil in the grid circuit, pole pieces in each of said coils defining a magnetic core, anopening in said coreadapted to be closed by a test sample of magnetically permeable material to physically close the ma netic circuitof said coils, means associated with said primary coil providing a predetermined frequency of resonance of a value less than 60 cycles per second in the plate circuit, means'for biasin said grid to provide oscillationin said oscillator when the test sample is in physical contact with said pole pieces, a voltage measuring device for measuring at least a part of the voltage between said grid and said cathode, the biasing means for said grid comprising a resistor in the cathode circuit of said tube electrically in series with the cathode and plate thereof across a source of supply voltage wherein positive voltageis supplied to -the plate and the negative terminal of said source is connected to oneend of said resistor, the other end being connected to said cathode, and means for reducing said-resistance to a value to sustain oscillations in said oscillator when the test piece is removed from said pole pieces comprising a relay having a normally closed contact through which a point between, the ends of said resistor 'may be connected to the negative, a relay coil for actuating said contact and causing opening thereof, a separate source of energy for energizing said relay coil, a voltage divider across said source of energy, and nieans'for connecting said coil to a small voltage portion of said voltage divider,

and an electrical switch actuable when a test sample is in physical contact with said pole pieces a and connected-electrically across a large voltage portion of said voltage divider whereby said contact is open only when said relay is energized by engagement of a test sample with said pole pieces,

and a manually actuable switch in series with a resistance of relatively low value disposed in parallel with said cathode resistance whereby the biasing on said grid may be suddenly and manually changed to initiate oscillations in said oscillator.

ROBERT SIDNEY SEGSWORTH.

References Cited in the file of this patent UNITED STATES PATENTS Hudson May 6, 1952 

